Jonathon, I understand the basics of machine structure and resonance and that I may need to add dampers at some point, however the motor itself is noticeably vibrating at very low speeds when it isn't even bolted to anything. The machine castings and framework are obviously amplifying the vibration but I think that will always be the case until the motor is made stable.

Regarding the drives and motors, it wasn't a case of "I blame the Chinese", the question I was asking is could it be a problem due to the low cost setup? At the end of the day, you get what you pay for, etc, etc. I bought the motors, drives, BOB and PSU as a 3-axis kit from Zapp a few years ago. If I was buying again, I'd probably buy the parts individually via eBay or AliExpress but go for better quality. Having said that, there seems to be plenty of others using the same setup and not having any issues.

Jonathon - I believe you use (or have used) LinuxCNC? Have you used it with these motors and drives? If so, maybe you could share a known working .ini file? The LinuxCNC latency/jitter test on my PC settles at 15600ns (with CPU at 100% load), so I have this set at 16000 in stepconf. I'm guessing this may be causing the RTAPI error but don't yet know enough about the system to understand what's going on.